Traditionally, electronic apparatuses (devices) such as personal computers, digital cameras and mobile terminals are each configured so that a battery pack (battery device) that stores a plurality of rechargeable battery cells (for example, lithium ion secondary battery cells) in a single container may be attached to the electronic device.
Various techniques have been developed for battery packs. For example, the following technique is known. In order to enable a battery pack with a simple configuration to be replaced when a battery runs out, a primary battery and a secondary battery are provided in the battery pack, and a connection terminal of the primary battery and a connection terminal of the secondary battery are point-symmetrically located.
Japanese Laid-open Patent Publication No. 2010-140857 is an example of related art.
The life of a battery pack is largely affected by thermal stress. However, when the battery pack is fixedly installed in a given location of an electronic device, the distance between a heat source (for example, a central processing unit (CPU)) included in the electronic device and each cell arranged in the battery pack is different for each cell. Thus, the life of the whole battery pack is determined based on a single cell that is closest to the heat source (that is, subjected to the highest thermal stress), and the life of the battery pack is shorter than a battery pack in which the amounts of heat received by cells are equal. A short life of the battery pack increases the running cost of the electronic device. In addition, because lithium, which is a raw material for lithium ion batteries that are frequently used as cells, is rare, there is a concern about the depletion of lithium in the future. From the perspective of protection of the Earth's resources, it is not desirable to reduce the life of a battery in which lithium is used. In order to equalize the amount of heat received by the cells, one method considered is to pack the battery pack with a high thermal conducting material. However, this causes an increase in cost and is not preferable.